Disconnecting switch for force-cooled isolated phase bus

ABSTRACT

A disconnecting switch for a force-cooled isolated phase bus comprises means for interrupting magnetizing currents when the switch is opened. The interrupting means comprises a vacuum-type circuit interrupter located in the space between the bus conductor and its surrounding enclosure. The bus conductor comprises a plurality of bus sections, one of which is movable to establish a gap in the bus conductor and to actuate a cam for controlling the vacuum interrupter. When the gap in the bus conductor is established, a shunting path extends through the closed vacuum interrupter until the cam allows the vacuum interrupter to open. The cam includes an auxiliary portion movable with respect to the rest of the cam for maintaining the continuity of the shunting path through the interrupter until the interrupter opens.

United States Patent 1 Miller [451 Oct. 31, 1972 DISCONNECTING SWITCH FOR FORCE-COOLED ISOLATED PHASE BUS Inventor: Richard H. Miller, Berwyn, Pa. Assignee: General Electric Company Filed: Aug. 9, 1971 Appl. No.2 170,064

US. Cl ..200/144 B, 200/ 146 R Int. Cl... ..H0lh 33/66 Field of Search..... ..200/144 B, 146 R, 145 R References Cited UNITED STATES PATENTS 8/ 1961 Heberlein et al...200/ 146 R X 1 0/ 1970 Fohrhaltz ..200/ 144 B 2/1971 Kohler ..200/l44 B 3/ 1971 Perkins et al ..200/ 144 B Primary Examiner-Robert S. Macon Attorney-J. Wesley Haubner et al.

[5 7] ABSTRACT A disconnecting switch for a force-cooled isolated phase bus comprises means for interrupting magnetizing currents when the switch is opened. The interrupting means comprises a vacuum-type circuit interrupter located'in the space between the bus conductor and its surrounding enclosure. The bus conductor comprises a plurality of bus sections, one of which is movable to establish a gap in the bus conductor and to actuate a cam for controlling'the vacuum interrupter. When the gap in the bus conductor is established, a

shunting path extends through the closed vacuum interrupter until the cam allows the vacuum interrupter to open} The cam includes an'auxiliary portion movable with respect to the rest of the cam for maintaining the continuity of the shunting path through the interrupter until the interrupter opens.

6 Claims, 3 Drawing Figures 7 PATENTEDHEI31 \m 3.701; 866

SHEET 2 BF 2 DISCONNECTING SWITCH-FOR FORCE-COOLED v ISOLATED PHASE BUS BACKGROUND OF THE INVENTION This invention relates to a disconnecting switch for a force-cooled isolated phase bus and,'more particularly, relates to a switch of this type which is capable of interrupting magnetizing current. v

A widely-used type of device for interrupting mag netizing currents is an interrupting device that comprises an arc chuteand a puffer fordeveloping gas flow that drives low current arcs into the chute. In such a device thearcing products resulting from interruption are exhausted from the chute at its exhaust end. Consideration has been given to using this type of interrupting device incombination with a telescoping disconnect switch in an isolated phase bus for the purpose of interrupting magnetizing currents'when the telescoping disconnect switch is opened. But if such an interrupting device is located within the usual enclosure of the isolated phase bus, a number of significant problemsare encountered, particularly if the bus is ,of the force cooled type. A major problem is thatthe gas stream which is used for force-'coolingcan interfere with aninterrupting operation. If this gas stream is counter to the pumping direction of the puffer or to the direction of exhaust from the-arc chute, it :will impede such flow, and this can detract from the interrupting capabilities of the interrupting device.

SUMMARY An object of my invention is to provide within the enclosure of a force-cooled isolated phase bus interrupting device for magnetizing currents which is unaffected by the gas stream that is used for cooling the bus.

Another object is to provide an interrupting device for such an isolated phase bus application which can perform its required interrupting function without introducing significant arcing products into the gas stream that is used for cooling the bus. The gas in this stream 'must'have a high dielectric'strength', and the presence of arcing products would detract from this dielectric strength.

Another object is to provide a relatively simple mechanism for maintaining intact a shunting path through the interrupting device until suchtime as the interrupting device has operated to interruptthe magnetizing current flowing therethrough upon establishment of a gap in the bus conductor.

in carrying out the invention in one form, I provide an isolated phase bus comprising an enclosure at ground potential, a high potential conductor within the evacuated envelope and a pair of relatively movablecontacts located therein. For actuating one of the contacts, a blade is pivotally mounted on the second stationary bus section, and suitable means is provided for operating the blade in response to movement of the movable bus section. When the movable bus section is in its closed, bridging position, the blade is in a first position where a cam thereon holds the vacuum interrupter contacts in engagement. When the movable bus section is in its fully open positiomthe blade is in a second position widely spaced from the vacuum interrupter. Means responsive to blade motion is provided v ofjthe invention.

for rapidly separating the contactsof the interrupter when the blade is moved out of its first position toward its second position. The cam includes an auxiliaryportion movable with respect to the rest of the cam which maintains the continuity of the shunting path through the interrupter while the contacts are separating.

I BRIEF DESCRIPTION OF THE DRAWINGS For a better understanding of the invention, reference may: be had to the following description taken in conjunction with the accompanying drawings, wherein: Q Y 5 FIG. 1 is a sideelevational view partly in section showing a switching arrangement embodyingone form FIG. 2 is an enlarged view'of a portion of FIG. 1.

FIG. 3'is an enlarged diagrammatic view of certain portions of the switching arrangement during an opening operation. i

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT.

Referring now to FIG. '1, there is shown an isolated phase bus comprising a grounded metal enclosure 10,- a high-voltage conductor 12 within the enclosure, and insulators 14 and 15 for supporting the conductor within the enclosure in spaced relationship thereto. The bus is a force-cooled type of bus in which a cooling gas is enclosure and spaced therefrom, and means for causing which cooling gas passes is a vacuum-type circuit interrupter. This circuit interrupter comprises a highly forced in a direction axially of the conductor through the space between the conductor and the enclosure, as indicated by arrows 18. This gas flowserves to cool the enclosure. and conductor. v

Bus conductor '12 comprisesa pair of axially aligned tubular sections 20 and 21 having their adjacent ends spaced apart. Bridging the gap between the bus sections is a third bus section 22 of tubular form which is adapted to be moved axially of the bus conductor. When the bridging conductor 22 is in its solid line position ofFlG. 1, current is conducted between the bus section and bridging conductor 22 by means of a plurality of conductive fingers 25. These fingers 25 are suitably supported on bus section 20 and are arranged to makea slidable connection with the outer periphery of bridging conductor 22 when it is moved axially of the bus and when it is near its closed position shown in FIG.

1. Similar fingers 27 are mounted on bus section 21 and are adapted to make a slidable connection with the outer periphery of bridging section 22.

Bus sections 2.0, 22 and 21 and current-transfer fin gers 25, 27, taken together, constitute the current-carrying portion of a telescoping disconnect switch. In the solid-lines of FIG. 1, the switch is in its closed position. When bridging section 22 is moved axially of the conductor to the right, it slides in telescoping relationship within bus section 21, and the switch is thus opened. When the left hand end of the bridging section 22 has entered the dotted-line position of FIG. 1, a gap of sufficient length is present between the end of bridging section 22 and the stationary section to withstand the open-circuit voltage present between these parts. Closing of the switch is effected by returning -the bridging section to its solid-line position of FIG. 1.

A suitable operating mechanism (not shown) is provided for moving bridging section 22 betweenits open and closed positions. This operating mechanism is located, in part, within tubularsection 21 and in part outside the enclosure 10. These two parts of the operating mechanism are coupled together by a suitable insulator (not shown) extending across the space between the enclosure and the conductor.

For interrupting magnetizing currents when the telescoping disconnect switch 20-27 is opened, I'provide a vacuum-type interrupting device 30. As shown in FIG. 2, this interrupting device comprises a vacuumtype circuit interrupter 31 comprising a highly evacuated envelope 32. The envelope comprises a tubular casing of insulating material and a pair of end caps 3 suitably sealed to opposite ends of the casing.

Within evacuated envelope 32 is a pair of relatively movable contacts 36 and 37. Contact 36 is a stationary contact mounted on a conductive contact rod 36a that projects through the left hand end cap 35 in sealed relationship thereto. Contact 37, is a movable contact mounted on a conductive contact rod 37a that projects freely through an opening in right hand end cap35. A suitable flexible metallic bellows 39 provides a seal about the movable contact rod 37a and allows it to be moved axially without impairing the vacuum inside the envelope. A suitable bearing 40 acts as a guide for the movable contact rod 37a.

Vacuum interrupter 31 is of a conventional design (e.g., such as shown and claimed in US. Pat. No. 3,522,399Crouch) and is capable of interrupting the current therethrough in a conventional manner. -Accordingly, when contact37 is moved to the right out of engagement with contact 36, an arc is established between the two contacts. This are persists until the first natural current zero, at which time it vanishes and is prevented from reigniting by the high dielectric strength of the vacuum.

For supporting the vacuum interrupter 31, there is provided an insulator 40 which is suitably attached at its base to the tubular bus section 20. Secured to the top of insulator 40 is a supporting bracket 42 that comprises a vertically extending portion 43, ahorizontally extending portion 44 and a foot 45. The vertically extending portion 43 is suitably attached to the right hand end cap 35 of the vacuum interrupter.

For operating the vacuum interrupter, an "operating mechanism 50. is provided. This operating mechanism comprises a lever 52 which is pivotally mounted intermediate its ends on a stationary pivot 53 carried by bracket 42. At the lower end of lever 52, there is a rod 54 pivotally connected to lever 52 and extending freely through an opening in the foot 45 of bracket 42. A compression spring 55 for opening the interrupter surrounds rod 54. This spring 55 bears at one end against the stop 56 carried by the rod 54 and at-its other end against foot45.

4 Opening spring 55 is normally prevented from discharging to open the interrupter by a cam member 57. This cam member 57 cooperates with a follower in the form of a roller 58 carried at the distal end of an actuating link 59. Actuating link 59 is pivotally mounted at62 on lever 52 and at 63 on a guide'link 60. Guide link 60 is pivotally mounted at its lower end on bracket 42 by means of a stationary pivot 64.

When cam 57 is removed from its position of FIG. 2 to a non-interfering position with respect to follower 58, as will soon be explained, the opening spring 55 discharges, driving rod 54 to the left. This drives lever 52 in a clockwise direction, carrying actuating link 59 to the right and pivoting guide link 60 in a clockwise direction. After a predetermined amount of such closing movement, a projection 64 on guide link 60 engages a projection 66 carried by contact rod 37a. This engagement drives contact 37 to the right at high speed, thereby opening the interrupter.

, A closing operation is effected bycausing cam 57. to drive follower 58 to the left back into its position shown in FIG.'2. Such movement of follower 58 drives actuating link 59 to the left, transmitting contact closing force to movable contact rod 37a through a wipe spring 70. When the contacts engage, actuating link 59 continues moving to the left for a short distance, compressing wipe spring 70 and applying a hold-closed force to the contacts. The circuit interrupter is then in its fully closed position shown in FIG. 2.

For operating cam 57 so as to control opening and closing motion of vacuum interrupter 31, I provide a blade 72 of conductive material pivotally mounted on a conductive bracket 73 carried by bus section 21. At its distal end, blade 72 carries the cam 57. When blade 72 is swung in a clockwise direction form its solid-line position of FIG. 1 toward its dotted line position, cam 57 moves out of contact with'follower 58 to allow opening of the vacuum interrupter to occur in the manner described hereinabove.

When blade 72 is returned in a counterclockwise direction to the solid-line position of- FIG. --1-, cam 57 forces follower 58 to the left to effect closing of the vacuum interrupter. v V

For controlling motion of blade 72, a link 75 of insulating material is connected between the bridging section 22 of the bus conductor and the blade 72. Link 75 is pivotally connected .at one end to the bridging section' and pivotally connected at its opposite end to blade 72. When bridging bus section 22 is moved to the right from its solid-line position of FIG. 1 into its dotted line position, such motion is transmitted through link 75 to blade 72 to move the blade into its dotted line fully open position. Similarly, return of bridging section 22 to its solid-line closed position acts through link 75 to return blade 72 to its solid-line closed position.

During an opening operation of the telescoping switch 20-27, a current-carrying path is established through the interrupting device 30 and in shunt with the gap that is developed by the telescoping switch. A portion of this current-carrying path extends through a vertical conductor 82 between bus section 20 and the stationary contact rod 36a. Vertical conductor 82 is a metal strap that is welded at its lower end to bus section 20. At its upper end, conductor 82 carries a clamp 84 that electrically connects the conductor 82 to the contact rod The current-carrying path further includes a flexible conductive braid 86 (FIG. 2) that is electrically connected between bracket 42 and movable contact rod 37a. Also forming a part of the currentcarrying path is a conductive leaf spring 88 attached at its lower end to bracket 42 and bearing at its upper end on a portion of conductive roller 58.

' thereby maintaining an electrical connection between When-the telescoping switch20-27 is fully closed as shown in FIGS. 1 and 2, no current flows through the shunting path through interrupting device 30 because roller 58 rests on an insulating portionf90 of cam 57, thus forming an electrical discontinuity in the shunting path. But when cam 57 is moved upwardly from its position ,of FIGS. 1 and 2 during a switch-opening operation, roller 58 engages a metal portion of cam 57 to establish an electrical. connectionbetween cam 57 and roller 58. So long as this electrical connection is maintained, a current path is available through roller 58, cam 57, conductive blade 72-, bracket 73 and bus section 21 to complete the shuntingpath through interrupting device 30. To summarize, this shunting path extends through the following parts 82, 84, 36a, 36, 37, 37a, .86, 42, 88,- 58,57, 72, and 73. It is to be understood that the shunting path is completed at 58, 57 during an opening operation before bridging section 22 can move sufficiently to establish a gap between section 22 and fingers 25.

The shunting path through interrupter31 is maintained until contacts 36, 37 of the interrupter have fully separated, thereby interrupting the flow of current through the shunting path. For maintaining the electrical continuity of the shunting path while the movable contact 37 is moving through its opening stroke, cam 57 is provided with an auxiliary portion, or slider, 95. Slider 95 has an active surface 96 which is a continuation of the idler surface of cam 57. This slider is slidably mounted in a groove 97 in cam 57 and is biased in a downward direction by the tension spring 98. Tension spring 98 is secured at its lower end to a pin 100 on cam 57 and at its upper end to a pin 102 on slider 95. Pin 102 is slidably received in a slot 104 that extends generally parallel. to the bottom of groove 97. Cam member 57 is occasionally referred to hereinafter as the main cam portion and slider 95' as the auxiliary cam portion. When the cam 57 is moved upwardly through a predetermined travel, the lower end of the auxiliary cam portion or slider 95 reaches the solid-line position shown in FIG. 3, where the active surface 96 of slider 95 is almost completely disengaged from follower 58. Further upward movement of cam 57 and slider 95 causes complete disengagement of active surface 96 and follower 58, and'this allows the opening spring 55 to discharge and thereby drive roller 58 to the right into and through its dotted line position of FIG. 3. Such roller movement forces slider 95 upwardly in groove 97 against the bias of spring 98. During such roller movement, spring 98 is biasing the lower surface 105 of the slider into contact with roller 58, thus maintaining an electrical connection between these parts.

The opening spring 55, in discharging and driving roller 58 through its dotted line position of FIG. 3, also drives lever 60 ina clockwise direction, causing projection 64 thereon to impact against projection 66 on contact rod 37a, thereby driving contact rod 37a through a full opening stroke. During this entire stroke, the lower these parts, thus forcing the circuit to be broken at contacts 36, 37 rather than at the roller 58 and cam portion 95. Because the circuit is broken at contacts 36, 37 within the sealed envelope 32, there are no arcing products escaping into the surrounding atmosphere, thus assuring that the dielectric strength of this atmosphere is not impaired by any such arcing products.

Since circuit interruption takes place within a sealed chamber 32 that completely isolates the interrupting action from the surrounding air, interruption is unaffected by the cooling air flowing through the space between bus conductor 92 and enclosure 10. The isolatednature of the interrupter chamber makes it immaterial whether such cooling air is flowing to the left or. to the right, thus allowing some desirable design freedom. 6

When contacts 36, 37 of the interrupter separate, the

switch is separated from stationary section 20 by a sufficient distance so that there is little risk of avoltage breakdown between these parts 20 and 22. But separation of bridging section 22 from stationary section 20 is continued until the bridging section enters the dottedline position of FIG. I. When this occurs, the blade 72 has reached its generally vertical dotted-line position of FIG. 1.

Closing of the. switch is effected by returning bridging section 22 from its dotted line position of FIG. 1 to its solid-line position. This drives blade 72 in a clockwise direction, eventually causing the lower end 105 of the slider to engage roller 58. Further closing movement of blade 72 causes the main cam portion 57 to continue moving downward while slider '95 is restrained from such movement by roller 58, thus causing the slider to slide relative to the main cam portion 57 andtension the spring 98. After a predetermined amount of such movement, cam surface 106on main cam'portion 57 engages roller 58 and drives it to the left into its contact-closed position. When roller 58 enters its contact-closed position,the slider 95v is free to move downwardly relative to main .carn portion 57. Such downward movement takes place under the bias of spring 98, thereby resetting the slider to its position of FIG. 2.

One purpose of the auxiliary cam portion or slider 95 is to postpone an opening operation of the vacuum interrupter 31 during a switch-opening operation until a sufficient gap can be established between bridging section 22 of the bus conductor and stationary section 20. Without the slider, opening motion of the vacuum interrupter could begin as soon as the upwardly moving cam surface 106 reached the roller 58 during an opening operation, and this would be too soon to permit establishment of a sufficient gap length between bus sections 22 and 20. v

In the illustrated application-of my switch, closing of the switch always takes place under no-load conditions. Accordingly, there are no lower limits on the closing speed of the bridging section 22. I

Although my switching arrangement is especially applicable to a force-cooled type of bus, it is to be understood that the invention in its broader aspects is also applicable to a bus that has no provision for force-coolmg.

While I have shown and described a particular embodiment of my inventionQit will be obvious to those skilled in the art that various changes, and modifications may be made without departing from my invention in its broader aspects; and I, therefore, intend herein to cover all such changes and modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In an isolated phase bus comprising an enclosure at ground potential; a high potential conductor spaced fromsaid enclosure; insulators for supporting said conductor within said enclosures; means for causing cooling gas to flow through the space between the conductor and the enclosure; said conductor including first and second stationary sections that are axially spacedapart and a third section that normally bridges the space between said first two sections, provides an electrical connection therebetween, and is movable axially of the conductor in telescoping relationship withsaid second section to establish a gap between said first two sections; and shunting means providing a shunt path around said gap for magnetizing current flowing when said gap is established; said shunting means comprising:

a. -a vacuum-type circuit interrupter comprising a highly evacuated envelope and a pair of relatively movable contacts located therein and connected in said shunting path,

b. means for' mounting said envelope on saidfirst conductor section in the space between 'said conductor and said enclosure,

c. a blade pivotally mounted on said second conductor section and means for actuating said blade in response to movement of said movable conductor section, said blade having a first position occupied when said movable conductor section is in its closed bridging position and a second position occupied when said movable conductor section has been fully separated from said first conductor section,

d. cam means carried by said blade for holding said contacts in closed position when the movable, conductor section is in said bridging position, i

e. and opening means responsive to motion of said blade for rapidly separating said contacts when the blade passes through a predetermined intermediate position in moving from its first positio toward its second position,

f. said cam means including means for maintaining the continuity of said shunting path while said contacts are separating to interrupt said magnetizing current,

g. further. motion of said blade toward its second position after said contacts have separated acting to establish an isolating gap in said shunting path.

2. The combination of claim'l in which: i

a. a follower is coupled to one of said contacts for transmitting force between said cam means and said one contact when the follower is acted upon by said cam means,

b. said cam means comprises a main cam portion having an idler surface cooperating with said follower to hold said one contact in closed position during initial movement of said blade from its first toward its second position,

c. said cam means further comprises an auxiliary portion movable with respect to said main portion and having a normal position relative to said main portion wherein a first surface in the auxiliary portion constitutes an extension of said idler surface for continuing to hold said one contact in closed position after said idler surface has moved out ofengagement with said follower during blade movement from said first toward said second position,

d. said opening means acts to drive said one contact into its open position when said first surface of said auxiliary cam portion moves out of engagement with said follower,

e. said opening means, in driving said one contact into its open position, applies through said fol- I lower a force on said auxiliary camportion that is effective to move said auxiliary cam portion relative to said main portion,

f. said auxiliary cam portion has a second surface that engages said follower when said followerlis being moved by said openingmeans, and

g. biasing means is provided for holding said second surface in engagement with said follower during follower movement to maintain an electrical connection between said follower and said auxiliary cam portion.

3. The combination of claim 2 in which:

a. said biasing means returns said auxiliary cam portion to its normal position with respect to said main cam portion when said isolating gap is present in the shunting path,

b. return motion of said blade from said second toward said first position causes said auxiliary cam portion to engage said follower before said main cam portion engages the follower, p

c. further return motion of first position charges said biasing .means and displaces said auxiliary cam portionfrom its normal position with respect to said main cam portion,

d. said main cam portion has a closing surface thereon that acts on said follower during charging of said biasing means todrivesaid movable contact into engagement with said other contact, and

e. said biasing means acts when said contacts are engaged to discharge and return said auxiliary cam portion to its normal position with respect to said main cam portion.

4. In an isolated phase bus; a high potential conduca. ,a vacuum-type circuit interrupter comprising a highly evacuated envelope and a pair of relatively movable contacts therein connected in said shunting path,

b. means for mounting said envelope on said first conductor section,

c. a blade pivotally mounted on said second conductor section and means for actuating said blade in response to movement of said movable conductor section, said blade having a first position occupied cam portion constitutes an extension of said idler surface for continuing to hold said one contact in closed position after said idler surface has moved with said follower,

j. said opening means, in driving said one contact into its open position, applying through said follower a force on said auxiliary cam portion that is when said movable conductor section is in its effected to move said auxiliary cam portion relaclosed bridging position and a second position 00- tive to said main cam portion,

cupied when said movable conductor section has k. said auxiliary cam portion having a secondsurface been fully separated from said first conductor secthat' engages said follower when said follower is tion, t v beingmovedby said opening means, and

d. cam means'carried by said blade for holding said l. biasing means for holding said second surface in contacts in closed position when the movable bus engagement with said follower during follower I section is in said bridging position, movement to maintain an electrical connection e. opening means responsive to motion of said blade between said follower and said auxiliary cam porfor rapidly separating said contacts when the blade tion, passes through a predetermined intermediate m. further motion of said bladetoward said second point in moving from its first position toward its position after said contacts have separated acting second position, v to establish an isolating gap in said shunting path.

f. a follower coupled to one of said contacts for trans 5. The combination of claim 1 in which:

mitting force between said cam means and said a. there is provided for controlling motion of said one one contact when the follower is acted upon by contact a follower coupled to said one contact and said cam means, engaging said cam means when said contacts are in g. said cam means comprising a main cam portion engagement,

having an idler surface cooperating with said folb. said cam means containing a portion of insulating lower to hold said one contact in closed position materialthat is engaged by said follower when said during initial movement of said blade from its first contacts are in engagement and said third conducto its second position, tor ction is in its b r id 'ng position h. said cam means further comprising an auxiliary Sal a mammal, mtemfpts portion movable with respect to Said main portion continuity of sa d shunting path when said ti lll'd and having a normal position relative to said main conductor, Secuon m 'bndgmg P cam portion wherein a first surface on the auxiliary whereby to block current flow through Shunt ing path when said third conductor sectionis in its bridging position. 6. The combination of claim 5 in which initial movement of said third conductor section from its bridging position toward its fully open position causes said follower to engage an electro-conductive portion of said out of engagement with said follower during blade movement from said first toward said second posi- 3 tion, s

i. said opening means acting to drive said one contact into its open position when said first surface of said Lil said cam and follower.

cam, thereby completing said shunting path through auxiliary cam portion moves out of engagement 

1. In an isolated phase bus comprising an enclosure at ground potential; a high potential conductor spaced from said enclosure; insulators for supporting said conductor within said enclosures; means for causing cooling gas to flow through the space between the conductor and the enclosure; said conductor including first and second stationary sections that are axially spaced-apart and a third section that normally bridges the space between said first two sections, provides an electrical connection therebetween, and is movable axially of the conductor in telescoping relationship with said second section to establish a gap between said first two sections; and shunting means providing a shunt path around said gap for magnetizing current flowing when said gap is established; said shunting means comprising: a. a vacuum-type circuit interrupter comprising a highly evacuated envelope and a pair of relatively movable contacts located therein and connected in said shunting path, b. means for mounting said envelope on said first conductor section in the space between said conductor and said enclosure, c. a blade pivotally mounted on said second conductor section and means for actuating said blade in response to movement of said movable conductor section, said blade having a first position occupied when said movable conductor section is in its closed bridging position and a second position occupied when said movable conductor section has been fully separated from said first conductor section, d. cam means carried by said blade for holding said contacts in closed position when the movable conductor section is in said bridging position, e. and opening means responsive to motion of said blade for rapidly separating said contacts when the blade passes through a predetermined intermediate position in moving from its first position toward its second position, f. said cam means including means for maintaining the continuity of said shunting path while said contacts are separating to Interrupt said magnetizing current, g. further motion of said blade toward its second position after said contacts have separated acting to establish an isolating gap in said shunting path.
 2. The combination of claim 1 in which: a. a follower is coupled to one of said contacts for transmitting force between said cam means and said one contact when the follower is acted upon by said cam means, b. said cam means comprises a main cam portion having an idler surface cooperating with said follower to hold said one contact in closed position during initial movement of said blade from its first toward its second position, c. said cam means further comprises an auxiliary portion movable with respect to said main portion and having a normal position relative to said main portion wherein a first surface in the auxiliary portion constitutes an extension of said idler surface for continuing to hold said one contact in closed position after said idler surface has moved out of engagement with said follower during blade movement from said first toward said second position, d. said opening means acts to drive said one contact into its open position when said first surface of said auxiliary cam portion moves out of engagement with said follower, e. said opening means, in driving said one contact into its open position, applies through said follower a force on said auxiliary cam portion that is effective to move said auxiliary cam portion relative to said main portion, f. said auxiliary cam portion has a second surface that engages said follower when said follower is being moved by said opening means, and g. biasing means is provided for holding said second surface in engagement with said follower during follower movement to maintain an electrical connection between said follower and said auxiliary cam portion.
 3. The combination of claim 2 in which: a. said biasing means returns said auxiliary cam portion to its normal position with respect to said main cam portion when said isolating gap is present in the shunting path, b. return motion of said blade from said second toward said first position causes said auxiliary cam portion to engage said follower before said main cam portion engages the follower, c. further return motion of first position charges said biasing means and displaces said auxiliary cam portion from its normal position with respect to said main cam portion, d. said main cam portion has a closing surface thereon that acts on said follower during charging of said biasing means to drive said movable contact into engagement with said other contact, and e. said biasing means acts when said contacts are engaged to discharge and return said auxiliary cam portion to its normal position with respect to said main cam portion.
 4. In an isolated phase bus; a high potential conductor including first and second stationary sections that are axially spaced apart and a third section that normally bridges the space between said first two sections; said third section providing an electrical connection between said first two sections and being movable relative to said first two sections to establish a gap between said first two sections; and shunting means providing a shunting path around said gap for magnetizing current flowing when said gap is established; said shunting means comprising: a. a vacuum-type circuit interrupter comprising a highly evacuated envelope and a pair of relatively movable contacts therein connected in said shunting path, b. means for mounting said envelope on said first conductor section, c. a blade pivotally mounted on said second conductor section and means for actuating said blade in response to movement of said movable conductor section, said blade having a first position occupied when said movable conductor section is in its closed bridging position and a second position occupied when said movable conductor section has been fully separated from said first conductor section, d. caM means carried by said blade for holding said contacts in closed position when the movable bus section is in said bridging position, e. opening means responsive to motion of said blade for rapidly separating said contacts when the blade passes through a predetermined intermediate point in moving from its first position toward its second position, f. a follower coupled to one of said contacts for transmitting force between said cam means and said one contact when the follower is acted upon by said cam means, g. said cam means comprising a main cam portion having an idler surface cooperating with said follower to hold said one contact in closed position during initial movement of said blade from its first to its second position, h. said cam means further comprising an auxiliary portion movable with respect to said main portion and having a normal position relative to said main cam portion wherein a first surface on the auxiliary cam portion constitutes an extension of said idler surface for continuing to hold said one contact in closed position after said idler surface has moved out of engagement with said follower during blade movement from said first toward said second position, i. said opening means acting to drive said one contact into its open position when said first surface of said auxiliary cam portion moves out of engagement with said follower, j. said opening means, in driving said one contact into its open position, applying through said follower a force on said auxiliary cam portion that is effected to move said auxiliary cam portion relative to said main cam portion, k. said auxiliary cam portion having a second surface that engages said follower when said follower is being moved by said opening means, and l. biasing means for holding said second surface in engagement with said follower during follower movement to maintain an electrical connection between said follower and said auxiliary cam portion, m. further motion of said blade toward said second position after said contacts have separated acting to establish an isolating gap in said shunting path.
 5. The combination of claim 1 in which: a. there is provided for controlling motion of said one contact a follower coupled to said one contact and engaging said cam means when said contacts are in engagement, b. said cam means containing a portion of insulating material that is engaged by said follower when said contacts are in engagement and said third conductor section is in its bridging position, c. said portion of insulating material interrupts the continuity of said shunting path when said third conductor section is in its bridging position, whereby to block current flow through said shunting path when said third conductor section is in its bridging position.
 6. The combination of claim 5 in which initial movement of said third conductor section from its bridging position toward its fully open position causes said follower to engage an electro-conductive portion of said cam, thereby completing said shunting path through said cam and follower. 